Prior to the conception and subsequent development of this invention, it is generally well known in the art to use various type brake shoes having different compositions to achieve quite specific braking requirements. For example, these compositions may include cast iron and various other type friction materials that are specifically formulated for a number of predetermined applications.
It is further well recognized, in the brake shoe art, that these various types of friction material will normally exhibit a number of uniquely different friction characteristics. Such friction characteristics, for example, include both high friction material and low friction material which are usually selected on the basis of braking performance requirements.
Since braking performance is the prime function of brake shoes, use of such lower type friction material may be adequate for braking purposes. However, there is normally no consideration of providing a secondary beneficial function toward the reconditioning of a wheel tread surface that may have surface defects, such as shells or spalls. Removal of these surface defects will normally extend the useful life of a wheel that is in service.
A brake shoe surface could be used which would be aggressive as far as reconditioning the wheel surface; however, this design may not provide appropriate friction levels for braking and may also have a disadvantage of creating significant sparking during brake applications which could result in a hazardous condition.
Applicant is aware of another design which is a shoe material made entirely from the aggressive grinding type material, however, this shoe must be applied and then immediately removed after a very low speed brake application. Thus, there is a need for a reconditioning brake shoe that will not present a safety problem because of inappropriate friction performance or because of a sparking condition while the brake shoe is reconditioning the defective surface of a wheel tread and still further a brake shoe that can continue to be used for normal braking operations after the wheel tread has been reconditioned.